The present invention relates to the field of pointing devices for use with personal computers and, in particular, to methods and systems for implementing an improved sampling scheme that enables a greater dynamic range of optical components to be used in a computer mouse.
U.S. Pat. No. 5,256,913 to Sommer (xe2x80x9cthe ""913 patentxe2x80x9d) discloses electronic components and circuits used to sense motion differences in a computer mouse. As detailed in the ""913 patent, a mouse typically uses optical components, such as light emitting diode (LED) and phototransistor (PTR) pairs, to determine motion. However, these components have a large manufacturing variability. This variability can cause problems in determining motion because of the limited dynamic range in the mouse electrical system.
Various methods have been used in the past in order to overcome this manufacturing variability. One method has been to test and sort each optical component to make sure that the component matches the system""s requirements. LEDs and photodetectors (e.g. phototransistors) from the same manufacturer, made on the same day by the same machine may exhibit widely varying brightness and sensitivity. For example, some LEDs are brighter than others with the same amount of applied power. Similarly, some photodetectors can see the same amount of light better other photodetectors. In this method, bright LEDs are paired with weak photodetectors, and dim LEDs are paired with strong photodetectors. Consequently, the strengths and weaknesses of the optical components are balanced out. Thus, in this method, components are sorted by strength into bins and the manufacturer puts appropriately matched optical components into the mice.
Another method is to design complex electrical circuits that dynamically adjust the system gain in order to compensate for optical-component variability. For example, it is common to use resistors to control the strength of optical components and their corresponding signals. During manufacturing, a mouse circuit board is built and powered up. A test device measures the strength of the signals. Variable resistors are then adjusted to compensate for the strengths and weaknesses of the optical components.
Unfortunately, the above methods are difficult and expensive to use in production. Further, employing these methods to overcome manufacturing variability significantly increase the manufacturing cost per unit of each mouse. In addition, using these methods slows production of the mice, further negatively impacting profitability.
Accordingly, it is an object of the present invention to provide an improved mouse optical sampling scheme that enables a greater dynamic range of optical components to be used in a computer mouse.
The present invention can be broadly summarized as follows. In one embodiment, the present invention is a method of determining motion in a mouse that is used in conjunction with a computer. At least one counter state machine is used to control at least one PTR state machine. At least one PTR state machine is used at a sample rate to determine the appropriate output for the mouse. The sample rate is adjusted, preferably after each sample, in order to minimize the system sensitivity to poor duty cycle regulation. In addition, Tmin value(s) are adjusted in order to optimize the duty cycle for each PTR state machine. The mouse output is then provided to the computer. By optimizing the duty cycle for each PTR state machine and minimizing its sensitivity to poor duty cycle regulation, a greater dynamic range of optical components can be employed in the mouse.
Of course, the method and system of this embodiment may also include other additional elements and/or steps.
Other embodiments are disclosed and claimed herein as well.